Devices called atomic clocks have been known for several decades and are able to keep time with very high precision. Conventional atomic clocks use atoms in a gas phase that can undergo transitions that correspond in energy to electromagnetic radiation in the microwave part of the spectrum. In one example a tunable microwave cavity contains the gas and the cavity can be tuned such that the field in the cavity oscillates very stably at a frequency corresponding to the energy transition in question. The most precise clocks at present are based on atomic fountains of cold atoms such as caesium or rubidium. Recently there have been developments using oscillations at frequencies corresponding to the optical (visible) part of the electromagnetic spectrum.
The availability of very high stability frequency standards, and the time-keeping that they provide, is used in many fields, including the synchronization of communication networks and in positioning systems, such as the satellite-based global positioning system (GPS). Conventional atomic clocks are generally quite large, delicate and have significant power requirements while operating. Thus there are the problems of providing compact, reliable, portable, low power atomic clocks.
Some proposals have been made regarding using endohedral fullerenes in a solid state atomic clock, see for Example U.S. Pat. No. 7,142,066. However, there are still problems regarding reducing environmental influence on the time-keeping, especially in portable devices, and also problems with achieving practical measurement and control of such systems.
The present invention aims to alleviate, at least partially, some or any of the above problems.